The Pentax K-3 is the most refined K-mount SLR to date, offering fast autofocus and superb image quality. Its video autofocus implementation isn't the best, but it still manages to snag our Editors' Choice award.

The K-3 is a little slow to start and shoot at 0.9-second, but it's a speedy camera once it gets going. It can rattle off shots at 8.1 frames per second, and while it can't shoot forever, its burst capabilities are quite impressive. It captures 24 Raw+JPG, 25 Raw, or 27 JPG images before slowing down. Writing complete bursts to a SanDisk 95MBps memory card requires 34, 26, and 15 seconds respectively. Compare this with the Nikon D7100; it starts faster (0.2-second), but the D7100 can only shot in raw mode at 5fps, and only for about 6 shots. Full-resolution JPG capture is closer to the K-3—the Nikon captures 22 shots before slowing, but its speed tops out at 6fps there.

The 27-point autofocus system is quick. All save the leftmost and rightmost point are cross-type, which means that they analyze focus vertically and horizontally. This puts cross-type sensors across a wider area of the frame compared to the D7100; only 15 of its 51 points are cross-types sensors. With ample light the K-3 can lock focus and fire its shutter in as little as 0.05-second, but in very dim light the focus speed can slow to about a second; the D7100 matches the 0.05-second speed and is just a little bit faster in dim light at 0.9-second.

Contrast detection autofocus takes over when you switch to Live View, and the K-3 puts up impressive marks for a traditional SLR. In ample light it locks focus and fires in about 0.9 second, and it slows to 3.1 seconds in very dim light. The D7100 is a bit longer to focus in ample light (1.7 second), but slightly quicker in dim light (2.8 seconds). Neither offers the always-on phase detect focus system and seamless transition between the rear LCD and electronic viewfinder that you get with the Sony Alpha 77; that's likely a better choice for frequent Live View shooters and videographers who prefer autofocus.

The K-3's 24-megapixel image sensor omits an optical low-pass filter. This is a growing trend in digital cameras, as the OLPF detracts from image sharpness by its very design. The filter gives a slight blur to fine details, and is used to reduce the possibility of color moiré effects from showing up in images. Moiré is a rainbow-like artifact that can appear when shooting some fabrics or natural objects with intricate repeating patterns like feathers. If you're shooting a scene where moiré is going to be an issue, simply flip a setting in the menu and its shake reduction system will move the sensor just enough during the exposure to blur your image the same way that an OLPF would. It gives you access to the sharpness that a sensor without an OLPF can deliver when desired, and the ability to eliminate moiré at capture when that's the requirement.

I used Imatest to analyze images captured with the K-3 in our test studio. This review is of the K-3 as a body only, but it's also available in a kit with an 18-135mm lens. Pentax supplied its lineup of HD Limited prime lenses for review, including the only zoom in that series, the HD DA 20-40mm F2.8-4 ED Limited DC WR.

I also used Imatest to check images captured by the K-3 for noise. The camera lets you customize the level of noise reduction that is applied to JPG images, but to keep the playing field even all of PCMag's tests are performed using JPG output at default settings. The K-3 does a great job of keeping noise under control, recording images with less than 1.5 percent through ISO 3200. I took a close look at the JPG output from the K-3 on a calibrated NEC MultiSync PA271W display and was happy to see that image detail holds up at ISO 3200. The fine lines of a foreign banknote in our ISO test scene are still distinct here, although there is some loss of punch compared to the Raw image at the same setting; but color output can be adjusted to be a bit more punchy in camera if you prefer that look. There's a little more JPG noise (1.9 percent) at ISO 6400, but details still hold up. It's not until you get to ISO 12800 that the JPGs really start to suffer at default noise reduction settings.

If you opt to reduce or disable noise reduction, or better yet, shoot in Raw, you'll be able to push the camera further. The Raw output at ISO 12800 is shockingly good, and even though Raw ISO 25600 images are noticeably grainy, detail is quite impressive thanks to a rather fine noise pattern. The top sensitivity is ISO 51200; even when shooting in Raw mode the noise takes on a larger, chunkier pattern. It's something you could use to an aesthetic advantage, especially if you're a black-and-white shooter who yearns for the look of Tri-X or Tmax 3200. The K-3 delivers the best high ISO output I've seen from a 24-megapixel APS-C camera, handling high sensitivities better than the Nikon D7100 and Sony Alpha 77.

The camera records HD QuickTime video at 1080i60, 1080p30/25/24, or 720p60/50/30/25/24 quality. Footage is crisp and sharp, and the visual evidence of the rolling shutter effect is limited to very fast pans if you opt to shoot in 60fps; at slower frame rates it's evident in slower pans. There are some pro features, including audio level control, an external mic input, and a headphone jack for audio monitoring. Available video capture modes include program, aperture priority, sensitivity priority, or full manual, all of which allow you to adjust settings during recording.

The K-3 delivers the fastest video autofocus I've seen in a Pentax D-SLR. But it's not without its limitations—there's no continuous AF, so you have to press the AF button on the rear of the camera every time you want to refocus. The Canon EOS 70D still delivers the best video autofocus performance that we've seen in a traditional D-SLR, and if you're willing to give an EVF a try you can get even better video out of the Sony Alpha 77—complete with fast autofocus and 1080p60 capture. Despite the improvements in autofocus, it's probably best to look at the K-3 as a manual focus video camera, you'll get better results by pulling focus manually, especially when working with a lens with a nice, long focus throw like the 35mm DA Limited Macro or any of the classic manual focus K-mount lenses that can be mounted. Focus peaking, which highlights in-focus areas of the frame in white on the rear LCD, is available at all times to help you nail focus when working manually.

The K-3 joins the full-frame Nikon D800 in bringing USB 3.0 to a camera. The port is located under a flap on the left side of the body, along with a micro HDMI output port and a DC input connector, and a port for a wired remote control is on the right. There's also a standard PC sync socket which, along with the ability to run the camera directly off of a wall outlet via an optional AC adapter, makes the K-3 a solid choice for use in a studio. Each of the two SD slots supports both SDHC and SDXC cards.

The Pentax K-3 is an outstanding take on the traditional D-SLR. It's got a top-notch optical viewfinder, it focuses quickly, and delivers outstanding image quality in the most difficult lighting situations. It's also compact for its class, and is fully weather sealed when paired with the right lens. Its burst mode is a bit speedier than the outgoing winner in this category, the Nikon D7100, which also omits an OLPF. But the K-3 can combat moiré using its sensor shift shake reduction system, something that the D7100 can't. It's not a perfect camera, even though the video autofocus and recording features are the best that Pentax has delivered to this point, it still lags behind the Canon EOS 70D and Sony Alpha 77 on video capture. The K-3 earns our Editors' Choice award, and should be a top choice if you're in the market for a serious APS-C D-SLR. If you're already a Pentax shooter, there's no question that it's a worthwhile upgrade.

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